Crystalline Silica XRD Peak

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition

SILICA, CRYSTALLINE, by XRD (filter redeposition) 7500

SiO2 MW: 60.08 CAS: 14808-60-7 (quartz) RTECS: VV7330000 (quartz) 14464-46-1 (cristobalite) VV7325000 (cristobalite) 15468-32-3 (tridymite) VV7335000 (tridymite)

METHOD: 7500, Issue 4 EVALUATION: FULL Issue 1: 15 August 1990Issue 4: 15 March 2003

OSHA : quartz (respirable) 10 mg/m3/(%SiO2+2);cristobalite and tridymite (respirable) ½ the above

NIOSH: 0.05 mg/m3; carcinogenACGIH: quartz (respirable) 0.1 mg/m3

cristobalite (respirable) 0.05 mg/m3

tridymite (respirable) 0.05 mg/m3

PROPERTIES: solid; d 2.65 g/cm3 @ 0 °C; crystallinetransformations: quartz to tridymite@ 867 °C; tridymite to cristobalite@ 1470 °C; "-quartz to ß-quartz@ 573 °C

SYNONYMS: free crystalline silica; silicon dioxide

SAMPLING MEASUREMENT

SAMPLER: CYCLONE + FILTER(10-mm nylon cyclone, Higgins-Dewell (HD) cyclone, or aluminumcyclone + 5-:m PVC membrane)*see sampling section

FLOW RATE: Nylon cyclone: 1.7 L/min;HD cyclone: 2.2 L/min;aluminum cyclone: 2.5 L/min

VOL-MIN: 400 L -MAX: 1000 L

SHIPMENT: Routine

SAMPLE STABILITY: Stable

BLANKS: 2 to 10 per set (see step 13.g.)

BULK SAMPLE: High-volume or settled dust; toidentify interferences

TECHNIQUE: X-RAY POWDER DIFFRACTION ANALYTE: Crystalline SiO2

ASH: Muffle furnace or RF plasma asher or dissolve in tetrahydrofuran

REDEPOSIT: On 0.45-:m Ag membrane filter

XRD: Cu target X-ray tube, graphite monochromatorOptimize for intensity; 1° slitSlow step scan, 0.02°/10 secIntegrated intensity with backgroundsubtraction

CALIBRATION: :NIST SRM 1878a quartz, NIST SRM1879a cristobalite, USGS 210-75-0043tridymite suspensions in 2-propanol.

RANGE: 0.02 to 2 mg SiO2 per sample [2]

ESTIMATED LOD: 0.005 mg SiO2 per sample [2]

PRECISION (þr): 0.08 @ 0.05 to 0.2 mg per sample [1]ACCURACY

RANGE STUDIED: 25 to 2500 :g/m3 [1](800-L sample)

BIAS: None known

OVERALL PRECISION (ÖrT): 0.09 (50 to 200 :g) [1]

ACCURACY: ± 18%

APPLICABILITY: The working range is 0.025 to 2.5 mg/m3 for an 800-L air sample.

INTERFERENCES: Micas, potash, feldspars, zircon, graphite, and aluminosilicates. See APPENDIX.

OTHER METHODS: This is similar to the method in the Criteria Document [3] and P&CAM 259 [4] which has been collaborativelytested [1]. This method is similar, except for sample collection, to S315 [5,6]. Method P&CAM 109 [7,8,9], which incorporates aninternal standard, has been dropped. XRD can distinguish the three silica polymorphs and silica interferences can be eliminatedby phosphoric acid treatment. IR (methods 7602 and 7603) can also quantify quartz, cristobalite and tridymite if amorphorous silicaand silicates are not present in large amounts. However sensitivity is reduced if multiple polymorphs are present and secondarypeaks must be used. Crystalline silica can also be determined by visible absorption spectrophotometry (e.g., Method 7601), butpolymorphs can not be distinguished. Visible absorption methods also have larger laboratory-to-laboratory variabilty than XRD andIR methods and therefore are recommended for research use only [10].

SILICA, CRYSTALLINE, by XRD: METHOD 7500, Issue 4, dated 15 March 2003 - of 9


REAGENTS:

1. Silica Standards.

a. Quartz* (SRMs 1878a, 2950, 2951, 2958)

and Cristobalite* (SRMs 1879a, 2960,

2957), available from Standard Reference

Materials Program, Rm. 204, Bldg. 202,

National Institute of Standards and

Technology (NIST), Gaithersburg, MD

20899; www.nist.gov.

b. Tridymite* (210-75-0043) available from

U.S. Geological Survey, Box 25046, MS

973, Denver, CO 80225.

2. 2-Propanol*, reagent grade.

3. Desiccant.

4. Glue or tape for securing Ag filters to XRD

holders.

5. Optional: tetrahydrofuran (THF)* (if LTA or

muffle furnace are unavailable).

6. 1.5 % parlodion solution. (Dissolve 1.5 g of

parlodion* in isopentyl acetate* and dilute to

100 mL with isopentyl acetate.)

7. Optional (if ca lcite present): 25% v/v

concentrated hydrochloric acid* (ACS

reagent grade) in distilled water and

25-mm filters of PVC or cellulose ester

with pore size of 1 :m or less.

* See SPECIAL PRECAUTIONS.

EQUIPMENT:

1. Sam pler:

a. Filter: Polyvinyl chloride (PVC) filter, 37-

mm , 5.0-:m pore size supported with

backup pad in a two-piece, 37-m m

cassette filter ho lder (preferably,

conductive) held together by tape or

cellulose shrink band.

NOTE: Check each new lot of PVC filters

by analyzing one or more by this

method. For example, Gelman

VM-1 filters (all lots) were found

to be unacceptable because of

high ash and background. If THF

is used, check for com plete

dissolution by dissolving a blank

PVC filter and following steps 5c

through 8.

b. Cyclone: 10-mm nylon, H iggins-Dewell

(HD), Alum inum (Al), or equivalent [11].

2. Area air sampler: PVC membrane filter, 37-

mm diameter, 5-:m pore size; three-piece

filter cassette.

3. Sampling pumps with flexible connecting

tubing, capable of the following flow rates:

nylon cyclone, 1.7 L/m in; HD cyclone, 2.2

L/m in; Al cyclone, 2.5 L/min; and bulk

sampler, 3 L/min.

4. Silver mem brane filters, 25-mm diameter,

0.45-µm pore size, available from Sterlitech

Corp., 22027 70th Ave S, Kent, WA 98032-

1911; www.sterlitech.com.

5. X-ray powder diffractometer (XRD) equipped

with copper target X-ray tube, graphite

monochromator, and scintillation detector.

6. Reference specimen (m ica, Arkansas stone,

or other stable standard) for data

normalization.

7. Low-temperature radio-frequency plasma

asher (LTA) or m uffle furnace, or ultrasonic

bath ($150 W ), for filter preparation.

8. Vacuum filtration assembly and side-arm

vacuum flask with a 25-mm filter holder.

9. Sieve, 10-:m, for wet sieving.

10. Analytical balance (0.001 m g); magnetic

stirrer with thermally insulated top; ultrasonic

bath or probe; volumetric pipettes and

flasks; Pyrex crucibles with covers (muffle

furnace); 40-m L wide-mouth or 50-mL

centrifuge tubes (THF m ethod); desiccator;

reagent bottles with ground glass stoppers;

drying oven; polyethylene wash bottle.

11. Explosion-resistant hot plate.

12. Teflon sheet, 0.3 to 1 mm thick.



SPECIAL PRECAUTIONS: Avoid inhaling silica dust [3]. THF is extremely flammable and should be used

in a fum e hood. 2-Propanol, parlodion and isopentyl acetate are flamm able. Hydrochloric acid is corrosive

and should be used in a fume hood.

SAMPLING:

1. Calibrate each personal sampling pump with a representative sampler in line.

2. Sample at 1.7 ± 5% L/min with nylon cyclone or 2.2 ± 5% L/m in with HD cyclone for a total sam ple size

of 400 to 1000 L. Do not exceed 2 mg dust loading on the filter.

NOTE 1: Do not allow the sam pler assembly to be inverted at any time when using a cyclone. Turning

the cyclone to anything other than a horizontal orientation may deposit oversized material

from the cyclone body onto the filter.

NOTE 2: A single sampler/flow rate should be used for a given application. Sampling for both

crystalline silica and coal mine dust should be done in accordance with the

ISO/CEN/ACGIH/ASTM respirable aerosol sam pling convention. Flow rates of 1.7 L/min for

the Dorr-Oliver nylon cyclone and 2.2 L/min for the Higgins-Dewell cyclone have been found

to be optimal for this purpose. Outside of coal mine dust sampling, the regulatory agencies

currently use these flow rates with the Dorr-Oliver cyclone in the United States and the

Higgins-Dewell sampler in the United Kingdom. Though the sampling recommendations

presented in a NIOSH Criteria Document have been formally accepted by MSHA for coal

mine dust sampling, the Dorr-Oliver cyclone at 2.0 L/min with 1.38 conversion factor is

currently used in the United States for the purpose of matching an earlier sampling

convention [12]. In any case, a single sampler/flow rate should be used in any given

application so as to eliminate bias introduced by differences between sampler types and

sam pler conventions [11].

3. Take an area air sample or collect a settled dust sample, if dust in the work environment has not been

previously characterized.

SAMPLE PREPARATION:

4. Samples may be characterized by one of the following methods, as appropriate.

a. Interference check. Prepare area dust sample or settled dust bulk sample for XRD analysis by

mounting the collection sample directly on an XRD sam ple holder, or by depositing or redepositing

the dust on another filter for mounting, or by packing an XRD powder holder. Proceed to step 11.

b. Qualitative Analysis. Prepare the area air sample or settled dust sample for qualitative analysis

by grinding and/or wet sieving to best match the airborne dust particle size. W et sieve with a 10-:m

sieve, 2-propanol, and an ultrasonic bath [13], followed by evaporation of excess alcohol, drying in

an oven for 2 hours, and overnight storage in a desiccator. Deposit the end product on a filter

(steps 7-8) or pack in a conventional XRD powder holder.

NOTE 1: For quantita tive determ ination of % SiO 2, weigh out, in triplicate, 2 mg sieved dust,

transfer to a 50-m L beaker, add 10 mL 2-propanol, and continue with step 6.

NOTE 2: In a bulk sample, if there is an interfering compound(s) that renders the

identification and quantitation of quartz very difficult, the sample will need to be carefully

treated in hot phosphoric acid [14] to dissolve the interfering compound(s) and avoid the

loss of quartz. This treatment can be used to dissolve several 50-mg sample aliquots

in order to concentrate the quartz content for the purpose of lowering the LOD.

5. Use one of the following methods to prepare filter samples and blanks:

a. Low Temperature Ashing: Place the filters in 50-mL beakers within the low temperature asher

so that the sample exposure to the plasm a is optim ized. Ash according to manufacturer's

instructions. After ashing, carefully add 15 mL 2-propanol to each beaker; or

b. Muffle Furnace Ashing:

i. If the samples contain a significant amount of calcite (>20% of total dust loading), silica may be

lost due to formation of CaSiO 3. Remove the calcite by the following procedure: Place a 0.5-:m,

25-mm PVC filter in the filtration apparatus and clamp the filter funnel over it. Remove the

sample filter from the cassette, fold, and drop it on the 25-mm filter. Add 10 mL 25% v/v HCl and



5 mL 2-propanol to the filter funnel and allow to stand for 5 min. Apply vacuum and slowly

aspirate the acid and alcohol in the funnel, washing with three successive 10-mL portions of

distilled water. Release the vacuum. Carry both filters through the ashing step together.

ii. Place the filter samples in porcelain crucibles, loosely cover and ash in muffle furnace for 2 h at

600 °C (800 °C if graphite is present). Add several m L 2-propanol to the ash, scrape the crucible

with a glass rod to loosen all particles and transfer the residue to a 50-mL beaker. Wash the

crucible several more times and add wash to beaker. Add 2-propanol to the beaker to bring the

volume to about 15 mL; or

c. Filter Dissolution: Using forceps and a spatula, remove the filter from the cassette, fold the filter

three times, and place in the bottom of a 40- or 50-mL centrifuge tube. Add 10 mL THF and allow

to stand for at least 5 m in. Cap the centrifuge tube with aluminum foil to prevent contamination.

Gently agitate the centrifuge tube by hand or with a vortex mixer mak ing sure the THF does not go

near the top of the tube. Place the tube in an ultrasonic bath (water level 2.5 cm from top) for at

least 10 m in. (The filter should be totally dissolved.) Just prior to filtering, agitate the sample for

10 to 20 sec on a vortex mixer. Continue with step 6, substituting THF for 2-propanol and

centrifuge tube for beaker.

6. Cover the beaker with a watchglass and agitate in an ultrasonic bath for at least 3 min. Observe the

suspension to make sure that the agglomerated particles are broken up. W ash the underside of the

watchglass with 2-propanol, collecting the washings in the beaker.

7. Place a silver filter in the filtration apparatus. Attach the funnel securely over the entire filter

circumference. W ith no vacuum, pour 2 to 3 mL 2-propanol onto the filter. Pour the sample suspension

from the beaker into the funnel. After the transfer, rinse the beaker several times and add rinsings to

the funnel for a total volume of 20 mL. In order to minimize feathering of the sample outside the

deposition area, allow the suspension to settle for a few minutes prior to applying vacuum. Do not rinse

the chimney after the material has been deposited on the silver filter. Rinsing the chimney can disturb

the thin layer deposition.

8. Leave the vacuum on after filtration to produce a dry filter. Place 2 drops of 1.5% parlodion solution on

a glass slide. Remove the silver filter with forceps and fix the material to the filter by placing the bottom

side of the filter in the parlodion so lution. Place the saturated filter on top of the Teflon sheet which has

been heated on the hot plate at a low temperature setting. W hen thoroughly dry, mount the silver filter

in the XRD sample holder.

CALIBRATION AND QUALITY CONTROL:

9. Prepare and analyze at least 6 levels of standard filters.

NOTE 1: Calibration standards are limited to NIST and USGS certified standards of known purity,

particle size, and sample-to-sample homogeneity. At least 12 materials, including 5-:m Min-

U-Sil, previously used by laboratories throughout the United States and Canada, have been

evaluated, and none have been found to be acceptable alternatives to the certified standards

cited within this method [10]. Standard reference materials should be corrected for phase

purity.

NOTE 2: Crystalline silica methods require calibration standards of known purity, specific particle size

and distribution, and sample-to-sam ple homogeneity. Establishing traceability of secondary

calibration standards to the specified NIST and USGS primary standards requires the use

of measurement methods with better precision and accuracy than the XRD, IR and visible

absorption spectrophotometry methods comm only used in the industrial hygiene field can

provide. In addition, particle size distribution measurements have considerable error.

Therefore, the use of secondary calibration standards that are traceable to NIST and USGS

certified standards is not appropriate.

NOTE 3: NIST SRM 2950 calibration set ("-quartz) and NIST SRM 2960 calibration set (cristobalite)

may be useful for preparing working standards at known concentrations.

a. Prepare two suspensions of each analyte in 2-propanol by weighing 10 and 50 mg of the standard

material to the nearest 0.01 m g. Quantitatively transfer each to a 1-L glass-stoppered bottle using

1.00 L of 2-propanol.

b. Suspend the powder in 2-propanol with an ultrasonic probe or bath for 20 min. Immediately move

the bottle to a magnetic stirrer with thermally insulated top and add a stirring bar. Allow the solution

to return to room temperature before withdrawing aliquots.



c. Mount a silver filter on the filtration apparatus. Place several mL of 2-propanol on the filter. Turn

off the stirrer and shake vigorous ly by hand. Immediately remove the stopper and withdraw an

aliquot from the center at half-height of the 10 mg/L or 50 mg/L suspension. Do not adjust the

volume in the pipet by expelling part of the suspension. If more than the desired aliquot is

withdrawn, discard the aliquot in a beaker, rinse and dry the p ipet, and take a new aliquot. Transfer

the aliquot from the pipet to the silver filter, keeping the tip of the pipet near the surface but not

submerged in the delivered suspension.

d. Rinse the pipet with several mL 2-propanol, draining the rinse into the funnel. Repeat the rinse

several times.

e. Allow the suspension to settle for a few minutes prior to applying vacuum. Apply vacuum and

rapidly filter the suspension. Do not wash down the sides of the funnel after the deposit is in place

since this will rearrange the material on the silver filter. Leave vacuum on until filter is dry. Place

2 drops of 1.5% parlodion solution on a glass slide. Remove the silver filter with forceps and fix the

material to the f ilter by placing the bottom side of the filter in the parlodion solution. Place the

saturated filter on top of the heated Teflon sheet. W hen thoroughly dry, mount the silver filter in the

XRD sample holder. Prepare working standard filters, in triplicate, at e.g., 10, 20, 50, 100, 250, and

500 :g.

f. Analyze the working standards together with samples and blanks (step 12). The XRD intensities

for the working standards (step 12.d) are designated Ixo and are then norm alized (step 12.e) to

obtain Îxo. Correct the intensities of working standards >200 :g for matrix absorption (steps 12.f and

13).

g. Prepare a calibration graph (Îxo, vs :g of each standard).

NOTE: Poor repeatability (>10% above 0.04 mg silica) at any given level indicates that new

standards should be made. The data should lie along a straight line. A weighted least

squares (1/F2 weighting) is preferable.

h. Determine the slope, m, of the calibration graph in counts/:g. The intercept, b, on the abscissa

should be within ± 5 :g of zero.

NOTE: A large intercept indicates an error in determ ining the background, i.e., an incorrect

baseline or interference by another phase.

10. NOTE: The following procedure for absorption correction is not necessary in situations that have been

previously documented as requiring no corrections.

Select six silver mem brane filters as media blanks randomly from the same box of filters to be used for

depositing the samples. These will be used to test for sample self-absorption. Mount each of the media

blanks on the filtration apparatus and apply vacuum to draw 5 to 10 m L 2-propanol through the filter.

Remove, let dry, and mount on XRD holders. Determine the net normalized count for the silver peak,

îAg, for each m edia blank (step 12.g). Obtain an average value for the six m edia blanks, ÎAog.

NOTE: The analyst is a critical part of this analytical procedure [12]. A high level of analyst expertise

is required to optimize instrument parameters and correct for matrix interferences either during

the sample preparation phase or the data analysis and interpretation phase [15]. The analyst

should have some training (university or short course) in mineralogy or crystallography in order

to have a background in crystal structure, diffraction patterns and mineral transform ation. In

addition, an intensive short course in the fundamentals of X -ray diff raction can be useful.

MEASUREMENT:

11. Obtain a qualitative X-ray diffraction scan (e.g., 10 to 80 °22) of the area air sample (or bulk settled

dust) to determine the presence of free silica polymorphs and interferences (see APPENDIX). The

diffraction peaks are:

Mineral Peak (2-Theta Degrees)

Primary Secondary Tertiary

Quartz 26.66 20.85 50.16

Cristobalite 21.93 36.11 31.46

Tridymite 21.62 20.50 23.28

Silver 38.12 44.28 77.47



NOTE: There is an alternative to scanning an area air sample, settled dust sample, or ground bulk

sample to prove lack of contamination. A slow scan of the three main peaks of quartz (also

cristobalite and tridym ite if their absence has not been previously confirmed) on a personal air

sample, with verification that their intensity ratios are within 15% of pure quartz, is sufficient

evidence that other materials are not interfering in the silica determination.

12. Perform the following for each sample, working standard, and blank filter:

a. Mount the reference specimen. Determ ine the net intensity, Ir, of the reference specimen before

and after each filter is scanned. Use a diffraction peak of high intensity that can be rapidly but

reproducibly (Sr <0.01) measured.

b. Mount the sample, work ing standard, or blank filter. Measure the diffraction peak area for each

silica polymorph. Scan times m ust be long, e.g., 15 min (longer scan times will lower the limit of

detection).

c. Measure the background on each side of the peak for one-half the time used for peak scanning.

The sum of these two counts is the average background. Determine the position of the background

for each sample.

d. Calculate the net intensity, Ix, (the difference between the peak integrated count and the total

background count).

e. Calculate and record the norm alized intensity, îx, for each peak:

NOTE: Select a convenient normalization scale factor, N, which is approximately equivalent to the

net count for the reference specimen peak, and use this value of N for all analyses.

Normalizing to the reference specim en intensity compensates for long-term drift in X-ray tube

intensity. If intensity measurements are stable, the reference specimen m ay be run less

frequently and the net intensities should be normalized to the most recently-measured

reference intensity.

f. Determine the norm alized count, ÎAg, of an interference-free silver peak on the sample filter

following the same procedure. Use a short scan time for the silver peak (e.g., 5% of scan time for

analyte peaks) throughout the method.

g. Fie ld blanks may be analyzed by scanning the 2-theta range used for the analyte and silver peaks

to verify that contamination of the filters has not occurred. The analyte peak should be absent. The

normalized intensity of the silver peak should match that of the media blank. Each laboratory

should determine the specifics of field blank use for its application. W hen contamination does

occur, the reason should be investigated and appropriate action taken. In practice, contamination

of field blanks is extremely rare and usually is not consistent across filters. The analysis of blanks

may be abbreviated if experience indicates that contamination is not likely with current field and

laboratory operations; however, occasional confirmation of non-contam ination is prudent.

CALCULATIONS:

13. Calculate the concentration of crystalline silica, C (mg/m 3), in the air volume sampled, V (L):

îx = normalized intensity for sample peak

b = intercept of calibration graph (Îxo vs. :g)

m = slope of calibration graph, counts/:g

f(t) = !R ln T/(1 ! TR) = absorption correction factor (Table 1)



R = sin (1Ag)/sin (1x)

T = îAg/(average ÎAog) = transmittance of sam ple

îAg = normalized silver peak intensity from sample

ÎAog = normalized silver peak intensity from media blanks (average of six values)

EVALUATION OF METHOD:

This method is based on P&CAM 259 which was collaboratively tested [1]. The testing included a

ruggedization step to test the effects of the use of muffle furnace or plasma asher (but not the use of THF),

shipment of samples, ashing time, and ultrasonication time. None of these factors was found to have an

effect. The method was shown to have no bias when referenced to the Talvitie spectrophotometric method

[14] and when all standards and sam ples were Min-U-Sil 5. The relative standard deviations (S r) for

intralaboratory, total measurement and overall (including sampling) variability are:

Analyte Level

(µg)

Measurement Precision

(Sr)

Overall Precision

(SrT)

Intralaboratory 50-200

20

10

0.08 [1]

0.20 [5]

0.28 [9]

Total (intra- and

interlaboratory)

50-200 0.17 [1] 0.29 [1]

REFERENCES:

[1] Anderson CC [9183]. Collaborative tests of two methods for determining free silica in airborne dust.

U.S. Departm ent of Health and Human Services, Publ. (NIOSH) 83-124.

[2] NIOSH [1983]. User check, UBTL, NIOSH Sequence #4121-M (unpublished)

[3] NIOSH [1974]. Criteria for a Recommended Standard: Occupational Exposure to Crystalline Silica.

U.S. Departm ent of Health, Education, and W elfare, Publ. (NIOSH) 75-120.

[4] NIOSH [1979]. Silica, crystalline: Method P&CAM 259. In: Taylor DG, ed., NIOSH Manual of Analytical

Methods, 2nd ed., Vol. 5. Cincinnati, OH: U.S. Department of Health, Education, and W elfare, Publ.

(NIOSH) 79-141.

[5] Ibid, Vol. 3, S315. U.S. Department of Health, Education, and W elfare, Publ. (NIOSH) 77-157-C (1977).

[6] NIOSH [1977]. Documentation of the NIOSH Validation Tests. S315, U.S. Department of Health,

Education, and W elfare, Publ. (NIOSH) 77-185.

[7] NIOSH [1977]. Silica (XRD): Method P&CAM 109. In: Taylor DG, ed., NIOSH Manual of Analytical

Methods, 2nd ed., Vol. 1. Cincinnati, OH: U.S. Department of Health, Education, and W elfare, Publ.

(NIOSH) 77-157-A.

[8] Bumsted HE [1973]. Determ ination of a lpha-quartz in the respirable portion of airborne particles by X-

ray diffraction. Am Ind Hyg Assoc J 34:150.

[9] Peters ET [1976]. Evaluation of the NIOSH X-ray diffraction method for the determination of free silica

in respirable dust. Final Report, NIOSH Contract CDC-99-74-51.

[10] Eller PM, Feng HA, Song RS, Key-Schwartz RJ, Esche CA, Groff JH [1999]. Proficiency analytical

testing (PAT) silica variability, 1990-1998. Am Ind Hyg Assoc J 60(4):533-539.

[11] Key-Schwartz RJ, Baron PA, Bartley DL, Rice FL, Schlecht PC [2003]. Chapter R, Determination of

airborne crystalline silica. In: NIOSH Manual of Analytical Methods, 4 th ed., 3 rd Suppl. Cincinnati, OH:

U.S. Departm ent of Health and Human Services, Public Health Service, Centers for Disease Control

and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No.

2003-154.

[12] Inhaled Particles and Vapours [1961]. Pergamon Press, Oxford, U.K.

[13] Kupel RE, Kinser RE, Mauer PA [1968]. Separation and analysis of the less than 10-micron fractions

of industrial dusts. Am Ind Hyg Assoc J 29:364.



[14] Talvitie NA [1951]. Determination of quartz in presence of silicates using phosphoric acid. Anal Chem

23 (4).

[15] Hurst VJ, Schroeder PA and Styron RW [1997]. Accurate quantification of quartz and other phases by

powder X-ray diffractometry. Anal Chem Acta 337:233-252.

[16] W illiams DD [1959]. Direct quantitative diffractometric analysis. Anal Chem 31:1841.

[17] Abell MT, Dollberg DD, Crable JV [1981]. Quantita tive analysis of dust samples from occupational

environments using computer automated X-ray diffraction. Advances in X-Ray Analysis 24:37.

[18] Abell MT, Dollberg DD, Lange BA, Hornung RW , Haartz JC [1981]. Absorption corrections in X-ray

diffraction dust analyses: procedures employing silver filters. Electron Microscopy and X-Ray

Applications, V. 2, p. 115, Ann Arbor Science Publishers, Inc.

[19] Dollberg DD, Abell MT, Lange BA [1980]. Occupational health analytical chemistry: quantitation using

x-ray powder diffraction. ACS Symposium Series, No. 120, 43.

[20] Altree-Williams S, Lee J, Mezin NV. Qualitative X-ray diffractometry on respirable dust collected on

nuclepore filters. Ann Occup Health Hyg 20:109.

[21] Leroux J, Powers C [1970]. Direct X-ray diffraction quantitative analysis of quartz in industrial dust f ilms

deposited on silver membrane filters. Occup Health Rev 21:26.

METHOD REVISED BY:

Rosa Key-Schwartz, Ph.D., Dawn Ramsey, M.S., and Paul Schlecht, NIOSH/DART.

APPENDIX: INTERFERENCES

Interferences include barite, micas (muscovite, biotite), potash, feldspars (microcline, plagioclase),

montmorillonite, sillimanite, zircon, graphite, iron carbide, clinoferrosillite, wollastonite, sanidine, leucite,

orthoclase, and lead sulfide.

The patterns for three forms of aluminum phosphate [JCPDS 10-423, 11-500, 20-44] are practically identical

to those of quartz, cristobalite and tridymite, respectively. The quartz secondary and cristobalite primary

peaks are c lose; cristobalite secondary peak is overlapped by a quartz peak; tridymite, if present in sufficient

quantity, will interfere with all of the main (primary, secondary and tertiary) quartz and cristobalite peaks.

Silver chloride, if present on the silver filter, interferes slightly with the primary quartz peak. Many of these

interferences occur in the presence of quartz; however, in a study of samples collected in 11 different

industries, Altree-W illiams [20] found no significant interferences.

The presence of elements such as iron can result in appreciable X-ray fluorescence which leads to high

background intensity. A diffracted-beam m onochromator will minimize this problem.

If calcite is present, loss of quartz will occur when samples are ashed in a muffle furnace. See SAMPLE

PREPARATION (step 5.b) for procedure to remove calcite.

If interferences with the primary silica peak are present, use a less sensitive peak. When overlaps are not

severe, a smaller receiving slit or chromium radiation may be used; however, a new calibration curve will be

necessary.



Table 1. Absorption correction factor as a function of transmittance for some silica-silver peak

combinations [16-21].

f(T) (at indicated degrees 2-2) Transmittance Silica 26.66 26.66 20.83 20.83 21.93 21.93 21.62 21.62

T Silver 38.12 44.28 38.12 44.28 38.12 44.28 38.12 44.28

1.00 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.00000.99 1.0071 1.0082 1.0091 1.0105 1.0087 1.0100 1.0088 1.01010.98 1.0144 1.0166 1.0184 1.0212 1.0174 1.0201 1.0177 1.02040.97 1.0217 1.0251 1.0278 1.0321 1.0264 1.0305 1.0268 1.03090.96 1.0292 1.0337 1.0373 1.0432 1.0355 1.0410 1.0360 1.04160.95 1.0368 1.0425 1.0470 1.0544 1.0447 1.0517 1.0453 1.05240.94 1.0445 1.0514 1.0569 1.0659 1.0541 1.0625 1.0548 1.06350.93 1.0523 1.0605 1.0670 1.0776 1.0636 1.0736 1.0645 1.07470.92 1.0602 1.0697 1.0772 1.0894 1.0733 1.0849 1.0743 1.08610.91 1.0683 1.0791 1.0876 1.1015 1.0831 1.0963 1.0844 1.09770.90 1.0765 1.0886 1.0982 1.1138 1.0932 1.1080 1.0945 1.10960.89 1.0848 1.0983 1.1089 1.1264 1.1034 1.1199 1.1049 1.12160.88 1.0933 1.1081 1.1199 1.1392 1.1137 1.1320 1.1154 1.13390.87 1.1019 1.1181 1.1311 1.1522 1.1243 1.1443 1.1261 1.14640.86 1.1106 1.1283 1.1424 1.1654 1.1350 1.1568 1.1370 1.15920.85 1.1195 1.1387 1.1540 1.1790 1.1460 1.1696 1.1481 1.17220.84 1.1286 1.1493 1.1657 1.1927 1.1571 1.1827 1.1595 1.18540.83 1.1378 1.1600 1.1777 1.2068 1.1685 1.1959 1.1710 1.19890.82 1.1471 1.1709 1.1899 1.2211 1.1800 1.2095 1.1827 1.21260.81 1.1566 1.1821 1.2024 1.2357 1.1918 1.2232 1.1946 1.22660.80 1.1663 1.1934 1.2150 1.2506 1.2038 1.2373 1.2068 1.24090.79 1.1762 1.2050 1.2280 1.2658 1.2160 1.2516 1.2192 1.25550.78 1.1863 1.2168 1.2411 1.2812 1.2284 1.2663 1.2319 1.27030.77 1.1965 1.2288 1.2546 1.2971 1.2411 1.2812 1.2447 1.28550.76 1.2069 1.2410 1.2683 1.3132 1.2540 1.2964 1.2579 1.30090.75 1.2175 1.2535 1.2822 1.3297 1.2672 1.3119 1.2713 1.31670.74 1.2283 1.2662 1.2965 1.3456 1.2806 1.3278 1.2849 1.33280.73 1.2394 1.2792 1.3110 1.3637 1.2944 1.3440 1.2989 1.34930.72 1.2506 1.2924 1.3259 1.3812 1.3084 1.3605 1.3131 1.36610.71 1.2621 1.3059 1.3410 1.3991 1.3226 1.3774 1.3276 1.38830.70 1.2738 1.3197 1.3565 1.4174 1.3372 1.3946 1.3424 1.40080.69 1.2857 1.3337 1.3723 1.4362 1.3521 1.4122 1.3576 1.41870.68 1.2979 1.3481 1.3885 1.4553 1.3673 1.4303 1.3730 1.43700.67 1.3103 1.3682 1.4050 1.4749 1.3829 1.4487 1.3888 1.45580.66 1.3230 1.3777 1.4218 1.4949 1.3987 1.4675 1.4050 1.47490.65 1.3359 1.3931 1.4390 1.5154 1.4150 1.4868 1.4215 1.49450.64 1.3491 1.4087 1.4567 1.5363 1.4316 1.5064 1.4383 1.51450.63 1.3626 1.4247 1.4747 1.5578 1.4485 1.5266 1.4556 1.53500.62 1.3765 1.4411 1.4931 1.5797 1.4659 1.5472 1.4732 1.55600.61 1.3906 1.4578 1.5120 1.6022 1.4836 1.5684 1.4913 1.57750.60 1.4050 1.4749 1.5314 1.6252 1.5018 1.5900 1.5098 1.59950.59 1.4198 1.4925 1.5511 1.6488 1.5204 1.6122 1.5287 1.62210.58 1.4349 1.5104 1.5714 1.6730 1.5394 1.6349 1.5481 1.64520.57 1.4504 1.5288 1.5922 1.6978 1.5590 1.6582 1.5679 1.66890.56 1.4662 1.5476 1.6135 1.7233 1.5790 1.6820 1.5883 1.69320.55 1.4824 1.5670 1.6353 1.7494 1.5995 1.7065 1.6092 1.71810.54 1.4991 1.6858 1.6577 1.7762 1.6205 1.7317 1.6306 1.74370.53 1.5161 1.6071 1.6807 1.8037 1.6421 1.7575 1.6525 1.76990.52 1.5336 1.6279 1.7043 1.8319 1.6642 1.7840 1.6751 1.79690.51 1.5515 1.6493 1.7285 1.8609 1.6870 1.8112 1.6982 1.82460.50 1.5699 1.6713 1.7534 1.8908 1.7103 1.8391 1.7220 1.8531

Crystalline Silica XRD Peak

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